I'm not intentionally using multiple threads, though the computer is dual core.

The error occurs within the loop; every so often, $array[0] contains the wrong value (yes, numeric), but always a previously used value. In tests, only about 20% of the values were wrong, the others right. And the second while loop solved the errors. I don't know how to explain that, really.

mytestfunc only reads values from the array, and does not change it.

Hi kjcdb8er, I just set up a little test to prove the fast assignment and reassignment of values in the array:

# 858508.pl
use strict;
use warnings;
use 5.010;

my @array_old = my @array = ( 1 .. 10e3 );

for my $i ( 0 .. $#array ) {
    my $buffer = $array[$i];
    $array[$i] = new_value();
    $array[$i] = $buffer;
 }

if( @array_old ~~ @array ) {
    say "arrays are equal";
} 
else {
    say "array are different";
}


sub new_value {
     rand();
}
[download]

This code creates an array of consequtive numbers from 1 to 10000 and changes every number to a random value and restores the initial value. I wasn't able to reproduce your problem. I suppose the problem you are facing is located on the different code part as you showed.

You can post the complete code so that others can run your code on their machine.